/* pngrio.c - functions for data input
 *
 * Last changed in libpng 1.4.1 [February 25, 2010]
 * Copyright (c) 1998-2010 Glenn Randers-Pehrson
 * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
 * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
 *
 * This code is released under the libpng license.
 * For conditions of distribution and use, see the disclaimer
 * and license in png.h
 *
 * This file provides a location for all input.  Users who need
 * special handling are expected to write a function that has the same
 * arguments as this and performs a similar function, but that possibly
 * has a different input method.  Note that you shouldn't change this
 * function, but rather write a replacement function and then make
 * libpng use it at run time with png_set_read_fn(...).
 */

#include "png.h"
#define PNG_NO_PEDANTIC_WARNINGS
#ifdef PNG_READ_SUPPORTED
    #include "pngpriv.h"

/* Read the data from whatever input you are using.  The default routine
 * reads from a file pointer.  Note that this routine sometimes gets called
 * with very small lengths, so you should implement some kind of simple
 * buffering if you are using unbuffered reads.  This should never be asked
 * to read more then 64K on a 16 bit machine.
 */
void /* PRIVATE */
png_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
{
    png_debug1(4, "reading %d bytes", (int)length);

    if (png_ptr->read_data_fn != NULL)
        (*(png_ptr->read_data_fn))(png_ptr, data, length);
    else
        png_error(png_ptr, "Call to NULL read function");
}

    #ifdef PNG_STDIO_SUPPORTED
/* This is the function that does the actual reading of data.  If you are
 * not reading from a standard C stream, you should create a replacement
 * read_data function and use it at run time with png_set_read_fn(), rather
 * than changing the library.
 */
        #ifndef USE_FAR_KEYWORD
void PNGAPI
png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
{
    png_size_t check;

    if (png_ptr == NULL)
        return;
    /* fread() returns 0 on error, so it is OK to store this in a png_size_t
     * instead of an int, which is what fread() actually returns.
     */
    check = fread(data, 1, length, (png_FILE_p)png_ptr->io_ptr);

    if (check != length)
        png_error(png_ptr, "Read Error");
}
        #else
/* This is the model-independent version. Since the standard I/O library
   can't handle far buffers in the medium and small models, we have to copy
   the data.
 */

            #define NEAR_BUF_SIZE 1024
            #define MIN(a, b) (a <= b ? a : b)

static void PNGAPI
png_default_read_data(png_structp png_ptr, png_bytep data, png_size_t length)
{
    png_size_t check;
    png_byte* n_data;
    png_FILE_p io_ptr;

    if (png_ptr == NULL)
        return;
    /* Check if data really is near. If so, use usual code. */
    n_data = (png_byte*)CVT_PTR_NOCHECK(data);
    io_ptr = (png_FILE_p)CVT_PTR(png_ptr->io_ptr);
    if ((png_bytep)n_data == data)
    {
        check = fread(n_data, 1, length, io_ptr);
    }
    else
    {
        png_byte buf[NEAR_BUF_SIZE];
        png_size_t read, remaining, err;
        check = 0;
        remaining = length;
        do
        {
            read = MIN(NEAR_BUF_SIZE, remaining);
            err = fread(buf, 1, read, io_ptr);
            png_memcpy(data, buf, read); /* copy far buffer to near buffer */
            if (err != read)
                break;
            else
                check += err;
            data += read;
            remaining -= read;
        }
        while (remaining != 0);
    }
    if ((png_uint_32)check != (png_uint_32)length)
        png_error(png_ptr, "read Error");
}
        #endif
    #endif

/* This function allows the application to supply a new input function
 * for libpng if standard C streams aren't being used.
 *
 * This function takes as its arguments:
 * png_ptr      - pointer to a png input data structure
 * io_ptr       - pointer to user supplied structure containing info about
 *                the input functions.  May be NULL.
 * read_data_fn - pointer to a new input function that takes as its
 *                arguments a pointer to a png_struct, a pointer to
 *                a location where input data can be stored, and a 32-bit
 *                unsigned int that is the number of bytes to be read.
 *                To exit and output any fatal error messages the new write
 *                function should call png_error(png_ptr, "Error msg").
 *                May be NULL, in which case libpng's default function will
 *                be used.
 */
void PNGAPI
png_set_read_fn(png_structp png_ptr, png_voidp io_ptr,
                png_rw_ptr read_data_fn)
{
    if (png_ptr == NULL)
        return;
    png_ptr->io_ptr = io_ptr;

    #ifdef PNG_STDIO_SUPPORTED
    if (read_data_fn != NULL)
        png_ptr->read_data_fn = read_data_fn;
    else
        png_ptr->read_data_fn = png_default_read_data;
    #else
    png_ptr->read_data_fn = read_data_fn;
    #endif

    /* It is an error to write to a read device */
    if (png_ptr->write_data_fn != NULL)
    {
        png_ptr->write_data_fn = NULL;
        png_warning(png_ptr,
                    "It's an error to set both read_data_fn and write_data_fn in the ");
        png_warning(png_ptr,
                    "same structure.  Resetting write_data_fn to NULL");
    }

    #ifdef PNG_WRITE_FLUSH_SUPPORTED
    png_ptr->output_flush_fn = NULL;
    #endif
}
#endif /* PNG_READ_SUPPORTED */